Conventionally, it is known that there are techniques which try to estimate popularity of things related to keywords on the basis of keywords used by users who use the Internet or the like. For example, these techniques count the number of times when a keyword is used to search for a web page or the like for each keyword and estimate the popularity of the keyword on the basis of the number of times when the keyword is used. For example, Patent Literature 1 describes a technique which detects a keyword that is not inputted during past counting periods but is newly inputted during a current counting period and which detects a keyword whose degree of change of the number of input times from a past counting period to the current counting period exceeds a predetermine range.